Our long-term goal is to understand the pathobiology of viral hepatitis. Hepatitis B virus (HBV) is the 4th most common infectious agent in humans worldwide. Chronic infection with HBV is tightly associated with the development of liver cancer. The mechanism of how HBV chronic infection is established and its pathogenesis remains to be fully explored. Recently, there has been increasing evidence that HBV chronicity may be influenced by the presence of genetic variants that evolve in patients as liver disease progresses. Since the invention of polymerase chain reaction technology, many HBV sequence variants have been reported. However, a common frustration in the research of HBV variants is that the majority of these reported sequence variants has no known functional significance and does not exhibit a strong phenotype distinctively different from the wild type virus. The most frequent missense mutation found in the HBV core antigen occurs at codon 97 in chronic carriers worldwide (in 83 percent hepatoma patients). Our recent functional characterization of this mutant uncovered a novel and strong phenotype, dubbed an "immature secretion" phenotype. Unlike wild type HBV, the secreted Dane particles of codon 97 mutants contain predominantly the immature form (lower molecular weight) of the HBV DNA genome. In this application, we propose 1) to extend our observation of the "immature secretion" phenomenon from tissue culture to patients and animal models. We also attempt to extend the "immature secretion" phenotype to other viral subtypes prevalent in different geographic locations. 2) to investigate the mechanism of "immature secretion" by both genetic and biochemical approaches. One of the several hypotheses to be tested is that "immature secretion" could be caused by hyper-efficient interactions between wild type envelope and mutant core proteins. 3) Finally, we will compare the infectivity of the highly frequent codon 97 mutants and wild type HBV via in vitro infection assays. Successful completion of this work will help understand the fundamental rules governing HBV morphogenesis and virion secretion, in addition to the important implications for chronic viral hepatitis as well as many other chronic progressive viral diseases.